Lubricant compositions

ABSTRACT

LUBRICANT COMPOSITIONS CONTAINING OIL-SOLUBLE COPOLYMERS OF ONE OR MORE ALKY ESTERS OF A C3-5 ALPHA, BETAVINYLIDENE MONOCARBOXYLIC ACID AND ONE OR MORE MONOHYDROXY ALKYL ESTERS OF A C3-5 ALPHA, BETA-VINYLLIDENE MONOCARBOXYLIC ACID, WHEREIN THE AVERAGE NUMBER OF THE CARBON ATOMS IN THE CH3-(CH2)N- GROUPS PRESENT IN THE ALKYL SIDE CHAINS, N BEING AT LEAT 9, IS FROM 12.5 TO 14.3, HAVE IMPROVED POUR POINTS, VISCOSITY INDICES AND DISPERSANT PROPERTIES.

United States Patent Ofiice 3,598,737 Patented Aug. 10, 1971 LUBRICANTCOMPOSITIONS Pieter H. Van der Meij and Johannes M. Wortel, Amsterdam,Netherlands, assignors to Shell Oil Company,

New York, N.Y.

No Drawing. Filed Apr. 17, 1969, Ser. No. 817,145 Claims priority,application Netherlands, Apr. 26, 1968,

6805941 Int. Cl. C10m H26, [/28 US. Cl. 252-56R ABSTRACT OF THEDISCLOSURE This invention relates to improved lubricant compositions andto novel oil-soluble copolymers contained therein. I The suitability ofa lubricating oil for use in internal combustion engines is dependent,among other properties, on its pour point, viscosimetric behavior, anddispersant ability. Since most lubricating base stocks do not inherent-'ly possess these properties to the extent required for use in presentday internal combustion engines, it is customary to addone or moreadditives to the lubricating medium to improve these characteristics.

Numerous polymeric additives have been proposed in the literature whichare capable of improving the pour point, viscosity index or dispersantability of lubricating oils. A select few ofjthese polymeric materialscan be classified as multi-functional additives, i.e., capable ofimproving more than one of these properties, and fewer still capable ofsimultaneously improving all three of the aforementionedcharacteristics. The present invention relates to such a class ofpolymeric additives, which because of their unique structuralconfiguration, have been un' expectedly found to significantly reducethe pour points of lubricating oils and also improve their viscosityindices and dispersant properties. The high activity of these polymericmaterials is attributed to a combination of their side chain length,molecular weight and polarity.

It has now been found that lubricating compositions comprising a majoramount of a lubricating oil and a minor amount, from 1 to 10% by weight,of an oil soluble copolymer of one or more alkyl esters of an alpha,

beta-vinylidene monocarboxylic acid and one or more monohydroxy alkylesters of an alpha, beta-vinylidene monocarboxylic acid, wherein theaverage number of carbon atoms in the Cl-l;,-(CH;),,- alkyl side chaingroups, n being at least 9, is from 12.5 to 14.3; the molar ratio of theunits derived from alkyl esters to those derived from hydroxy alkylesters is 10 to 025-5; and the molecular weight M, of the copolymer isfrom 100,000 to 2,000,000, have improved pour point, viscosimetric, anddispersant properties. It was further found that the above-statedlimitations, particularly the length of the alkyl side chains, wasextremely critical in respect to the activity of the polymeric additivesof the invention.

Comparison ofthe pour point depressing action in lubricating oil ofpolymers according to the invention with similar polymers in which theaverage number of carbon atoms of the CH;--(CH;),, groups present in thealkyl side chain, n being at least 9, is more than 14.3,

Claims for example 14.6 or 15.0, or less than 12.5, for example 12.0,shows that the polymers according to the invention are capable ofdepressing the-pour point of the lubricating oil to a much greaterextent. Preferred polymers according to the invention are those in whichthe average number of carbon atoms of the CH -(CH groups present in thealkyl side chains, n being at least 9, is from 13.0 to 14.1.

The molecular weight of therpresent polymers may vary within widelimits. Often polymers are selected with a molecular weight M, of atleast 100,000 and at most 2,000,000, in particular polymers with amolecular weight M of at least 250,000 and at most'l,250,000. Animportant further aspect of polymeric lube oil additives is theirresistance to degradation by shear in the engine. if polymeric lube oiladditives haveinsufiicient shear stability, one of the consequences isthat the viscosity of the lubricating oil composition in which they areincorporated diminishes during use of the composition in the engine. ithas been found that the molecular weight of the present polymers playsan important part as far as their shear stability is concerned. Polymersaccording to the invention have ahigh shear stability, especially iftheir molecular weight M is below 750,000.

The molar ratio of the units derived from the alkyl esters to thosederived from the hydroxy alkyl esters may vary within wide limits.Generally, for every 10 units derived from alkyl esters, the copolymersshould contain 0.25-5 units derived from .the monohydroxy alkyl esters.To assure satisfactory pourability of concentrates of the presentpolymers in oil, preference is given to polymers which for every 10units derived from the alkyl esters fewer than 3' units are derived fromthe monohydroxy alkyl esters. The use of the present polymers with lowpolarity is not only preferred from the standpoint of betterpourability, but also for another reason. If the polarity is lowered,the thickening power of the polymers increases, which means that lowermolecular weight polymers can be used to achieve the same viscositylevel. As previously noted, reduction of the molecular weight of thepresent polymers results in an increase of shear stability. However, toolarge a reduction of polar groups in the present polymers results in areduction of the dispersive power and the VI-improving action. In viewof the foregoing, preference is given to polymers according to theinvention which for every 10 units derived from alkyl esters at least 1and at most 3 units are derived from the hydroxy alkyl esters.

in principle the present copolymers can be prepared by two routes. It ispossible to prepare these copolymers directly by copolymerization of amixture of monomers consisting of one or more alkyl esters ofunsaturated monocarboxylic acids and one or more monohydroxy alkylesters of unsaturated monocarboxylic acids. The copolymers arepreferably prepared via an indirect route by copolymerization of amixture of monomers consisting of one or more unsaturated monocarboxylicacids and one or more alkyl esters of unsaturated monocarboxylic acidsand after treatment of the acid copolymers, in which the carboxylicgroups are converted'to COOR groups, in g which R represents amonohydroxy alkyl group.

The alkyl esters of monocarboxylic acids suitable for use as monomers inthe preparation of the present copolymers should consist of at leastmole percent of alkyl esters having an alkyl chain which contains agroup, n being at least 9.- Moreover, these alkyl esters should havesuch a chain length and be present in the monomer mixture in suchrelative proportions that the average number of carbon atoms of the CH(CI-1;),,-- groups present in the alkyl chains, n being at least 9, isat least 12.5 and at most 14.3. Examples of such monomers are alkylesters of unsaturated monocarboxylic acids in which an unbranchedsaturated hydrocarbon chain with at least carbon atoms such as n-decyl,n-dodecyl, ntetradecyl, n-hexadecyl, and n-octadecyl esters ofunsaturated monocarboxylic acids. Alkyl esters of unsaturatedmonocarboxylic acids in which a branched hydrocarbon chain occurs arealso suitable provided this branched hydrocarbon chain contains a Cli-(Cl m group, in which n is at least 9.

In addition to the aforesaid alkyl esters which must be present in themonomer mixture to be polymerized, the monomer mixture can contain otheralkyl esters of unsaturated monocarboxylic acids such as alkyl esterswith fewer than 10 carbon atoms in the alkyl chain or alkyl esters with10 or more carbon atoms in the alkyl chain, in which, however, aCH,-(CH,) group, with n being at least 9, is absent. Examples of suchmonomers are methyl, ethyl, n-butyl, iso octyl, and 2-mcthyldecyl estersof unsaturated monocarboxylic acids. Polymers prepared by using amixture of aikyimethacryiates consisting at least in part ofaikylmethacrylates which contain the group CH -(CH,),,, wherein n isll-l7 have been found to be very advantageous. The present copolymerscan be conveniently prepared from a mixture of alkylmethacrylates whichconsists at least in part of alkylmethacryiates derived from alcoholsobtained by a special hydroformulation process. The alcohols in questioncan be prepared by reacting oiefins with carbon monoxide and hydrogeninthe presence of a complex catalyst which contains in the molecule atransition metal with an atomic number of 23 to 85 and at least onemolecule of a biphyliic ligand which contains trivalentphosphorus,'arsine or antimony as catalyst. In this context a .biphyiiicligand is understood to mean a compound containing an element with anelectron pair which is capable of forming a coordination bond with ametal atom and which element is at the same time capable of acceptingelectrons from the metal, as a result of which the stability of thecomplex is increased. Highly favorable results may be obtained by usinga complex which contains cobalt, carbon monoxide and one or morephosphorus compounds.

Unsaturated monocarboxylic acids which are particularly suitable for usein preparing alkyl ester and hydroxy alkyl ester monomers are thosehaving 3 to 5 carbon atoms and alpha,beta-vinylidene unsaturation.Examples of such acids are acrylic acid, methacrylic acid, itaconic acidand crotonie acid. Esters of methacrylic acid have been found to beparticularly advantageous in forming the copolymeric additives of theinvention. 1

The monohydroxy alkyl esters are generally formed from theaforementioned unsaturated monocarboxylic acids and dihydric alcoholsoraiiphatic ethers. Preferably, the monohydroxy alkyl group of the estershould contain from two to five carbon atoms. Thus, suitable monohydroxyalkyl ester monomers include partial esters of dihydric alcohols such asethylene glycol with unsaturated monocarboxylic acids such as acrylicacid and methacryiic acid. Examples of such esters further includereaction products of cyclic ethers which in addition to an oxygen atomcontain two or three carbon atoms in the ring, such as ethylene oxideand trimethylene oxide with unsaturated monocarboxylic acids such asacrylic acid and methacryiic acid. Preference is given to copolymers offl-hydroxycthyl methacrylate. if the preparation of the presentcopolymers is effected via an indirect route, by copolymerization of amixture of monomers consisting of one or more unsaturated monocnrboxyiicacids and by tiftertrcntmcnt of the copolymers thus obtained, it ispreferred to use methacryiic acid as the unsaturated monocnrboxyiicacid. The aftertreatmcnt of the copolymers with free cnrboxyl groups asa result of which these groups are converted into -COOR groups, whereinR represents a monohydroxy alkyl group, can be carried out in variousways.

It is possible, for example, to react the copolymers proximatelycomplete,

having free carboxyl groups with dihydric alcohols such as ethyleneglycol. The after-treatment is preferably carried out by reacting thecopolymers having free carboxyl groups with cyclic ethers which inaddition to an oxygen atom contain two or three carbon atoms in thering, such as ethylene oxide and trimethylene oxide, in particularethylene oxide.

The preparation of the acid copolymers is preferably carried out insolution in the presence of a radical initiator such as an azo compoundor a peroxide. As is known, the relative proportion in which themonomers are incorporated into a growing copolymer molecule is dependenton the reactivity of the monomers in question. If these reactivitiesdiffer, the'molar ratio of the monomers in the mixture to be polymerizedwill change considerably as the copolymerization proceeds, since themore reactive monomer is incorporated more rapidly. The effect of thisis that the composition of the copolymer likewise changes continually.In general, it may be said that if no special measures are taken in thepolymerization of monomers which differ strongly in reactivity, productswith an extremely heterogeneous composition are obtained. A case inpoint occurs in the co-polymerization of unsaturated monocarboxylicacids and alkyl esters of unsaturated monocarboxyiic acids. It has beenfound, however, that the rates of incorporation of these monomers can bemade equal by carryingout the subject copolymerization in the presenceof a substance which associates with the unsaturated monocarboxylicacid. As a result of the equal rate of incorporation of the monomers themolar ratio of the incorporated monomers becomes the same as that of themonomers in the starting mixturerEligibie associating substances are,inter alia, aliphatic compounds containing an oxygen atom linked tocarbon such as alcohols, ethers, ketones and carboxylic acids.Preference is given to aliphatic alcohols such as methanol, ethanol,isopropanol and tert-butanol, in particular methanol. Suitable solventsin which the copolymerizations can be carried out are,

for example, benzene, toluene, or xylene, in particular toi-' uene.

In general, the polymerization of unsaturated monocarboxylic acids withalkyl esters of unsaturated monocarboxylic acids proceeds rapidly untila conversion of approximately 90% has been reached. However, continuedpolymerization to a conversion of -l00% is rather timeconsuming. It wasfound that the polymerization rate can be considerably increased if,after the conversion is ap an additional quantity of initiatorvaryingfrom ill-% by weight based on the quantity of initiator used at thebeginning of the polymerization is added to the reaction mixture.

The after-treatment of the copolymers with free carboxyl groups in whichthe carboxyl groups are converted into COOR groups wherein R representsa monohydroxy alkyl group, is preferably'carried out by means of acyclic ether, in particular ethylene oxide. This conversion can takeplace under the influence of a basic reacting substance as catalyst.Examples of suitable basic reacting substances include alkali metals,alkali metal oxides, alkali metal hydroxides, alkaline earth metals,alkaline earth metal oxides, alkaline earth metal hydroxides and organiccompounds such as trimethylamine, N-methyl morpholine, pyridine,quinoiine and fl-picoline. It is preferred to use a lithium compound ascatalyst. Examples of suitable lithium compounds are, inter alia,lithium hydroxide, lithium hydride, lithium alkoxides, lithiumcarbonate, and lithium acetate. Very favorable results may be obtainedby using lithium hydroxide as catalyst.

A variant of the alter-treatment described above is one in whichcontrary to the usual practice, the reaction of the acid copoiymcr'withthe cyclic ether is not carried out in the presence of a basic reactingsubstance as catalyst, but instead this catalyst is incorporated intothe acid polymer at the outset of the reaction. The incorporation of thecatalyst into the acid polymer can be effected by including in themixture of monomers from which the acid polymer is prepared; one or moresalts of basic reacting substances and unsaturated monocarboxylic acids.The acid copolymer resulting from the polymerization of this mixture ofmonomers can subsequently be reacted with a cyclic ether without usingany additional catalyst. Here again preference is given to lithiumsalts.

The reaction of the acid copolymer withthe cyclic ether can be carriedout at room temperature, but is preferably carried out at an elevatedtemperature, for example at a temperature between 95 and 130 C. If thefinal product is liquid, the reaction can take place without the use ofa solvent. If a solvent is used it can be either a polar or a non-polarsolvent. Thepolymer with free carboxylic acid groups shows a tendency,especially in a non-polar solvent, to form intermolecular hydrogen bondsas a result of which the viscosity increases sharply. For this reason itis preferred to carry out the reaction with the cyclic ether in thepresence of a polar substance which inhibits the formation ofintermolecular hydrogen bonds. A low-boiling aliphatic alcohol is veryconvenient for this purpose. A highly suitable medium for carrying outthe reaction is a mixtureof a low-boiling aliphatic alcohol and anaromatichydrocarbon.

In the preparation of the present polymeric compounds bycopolymerization of acid polymers followed by aftertreatmcnt with acyclic ether, it is not necessary to isolate the acid polymers beforereacting these with the cyclic ether. The cyclic ether may be addeddirectly to the reaction mixture obtained in the copolymerization. If inthe preparation of the acid polymer, use was made of an alcohol asassociating substance, this one-step process offers the additionaladvantage that the alcohol present in the reaction mixture also inhibitsthe formation of intermolecular hydrogen bonds in the acid polymer.

The lubricants in which the polymers according to this invention can beincorporated as additives may be mineral lubricating oils of varyingviscosity, synthetic lubricating oils or lubricating oils containingfatty oils. The polymers can also be employed in greases. The presentpolymers are of special importance for the improvement of minearlubricating oils or mixtures thereof. The polymers can be added to thelubricant as such or in the form of a concentrate obtained for exampleby mixing the polymers with a minor quantity of oil. The concentrationof the present polymers in the lubricants may vary within wide limits,for example from 0.1 to 10% by weight, more specifically 0.5 to 5% byweight.

In addition to the present polmyers, the lubricating compositions maycontain other additives such as antioxidants, anti-foaming agents,anti-corrosive agents. means for improving the lubricating action andother substances which are generally added to lubricants.

erization of a mixture of alkyl methacrylates and methacrylic acidfollowed by ethoxylation of the acid coply mers. For comparison threerelated copolymers (Polymers A-C) were also prepared by copolymerizationof a 'mixture of alkyl methacrylats and methacrylic acid followed byethoxylation of the acid copolymers; however, these three polymers didnot meet the criterion laid down in'the main claim in respect of thealkyl side chains. For illustrative purposes, the preparation of Polymer12 is described below. The preparation of the other polymers waseffected in the same manner.

Preparation of Polymer ,12

42.5% by weight of a mixture of alkyl methacrylatesand methacrylic acidin the ratio desired in the ultimate copolymer, were mixed with 12% byweight of methanol, 45.5% by weight of toluene and 0.165% by weight ofbenzoyl peroxide. The mixture was heated to 80' C. and

- in Table l.

111 this table use made of the following abbreviations: .C .MA=mixtureof alkyl methacrylates with 7-9 carbon atoms in the alkyl group.

carbon atoms in the alkyl group. These alkyl methacrylates were derivedfrom an alcohol mixture prepared by reacting oletins having 11-14 carbonatoms with carbon monoxide and hydrogen in the presence of a complexwhich contained cobalt and organically bound trivalent phosphorus. Theaverage number of carbon atoms of the CH (CH -"groups present in thealkyl chains, n being at least 9, was 12.9 for this mixture. I

n-C MA, n-CIflHA, n-C MA, 'n-C MA and 11- C MA=alky1 methacrylates withan unbranched'satw rated alkyl chain having 10, l2, 14, 16 and 18 carbonatoms respectively. f

HEMA=hydroxyethylmethacrylate.

The table also shows the molecular weight M of the polymers as well asthe average number of carbon atoms of the groups CH -(Cl-lfl present inthe alkyl side chains,wherein n is at least 9. This average number ofcarbon atoms is designated in the table with C TABLEI Molar composition01' the copolymers 1'01.

(511111 n CMMA t:.- ..\1,\ CNMA C hlA C MA HEM/t Mw cs sin a. 11 10 a01, 200, 000 1:1.

z 1'.- 10 11 10 is 470, 000 1:1. 7 z 112 10 11 10 111 200,000 13.;

The invention will now be demonstrated by means of 1 EXAMPLE 1! thefollowing examples. EXAMPLE 1 Thirteen copolymers according to theinvention (Polymers 1-13 shown in Table I) were prepared by copolym- Theeiiect of the present polymers on the pour point and the viscosirnetricproperties of a lubricating oil were examined by incorporating thepolymers in various concentrations into a distillate lubricating oil.The pour point C MA= -mixture of alkyl methacrylates with 12-15 I quenceV-A test. For comparison,

7 was determined by AST M method D 97.

TABLE II Vs 38 "x 100 Tour Composition oi the oil es. es. point, C.

Base oil 47. 2 6.64

Base oil plus- 1 1.6% by weight oi polymer A -0 1.67 by weight oipolymer 02.0 0 4. by weight oi polymer C 23 1.6 by weight at polymer 102. 3 0. it -32 1.5 by weight oi polymer 02. 0 9. 8 -32 1.6 by woig-itoi polymer 3... 01. 9 0.7 32 1.5 by weig 1t oi polymer 02. 0 0.0 -Zl21.5% by welt; ht oi polymer 5 02.3 0. 8 1.5 by weight oi polymer 0 02.1in. 0 a 20 1.5 n by weirt it oi polymer 7 01!. 2 i0. 0 -3'. 1.15 byweight at polymer 8 03.0 10.0 --:t'.' 1.6 by weight oi p0 ymer 0 02.70.0 -3' 4.07: by weight oi polymer 0 -t0 EXAMPLE III TABLE IIIConcentrate of polymer: Flow-out time, see. I 8 164 9 143 l 328 EXAMPLEIV The shear stability of the present polymers was determined in an Opelpump test. To this end they were incorporated in various concentrationsinto mineral lubricating oil with a V 100 C.=5.5 cs., to which had beenadded 8% by weight of a commercial additive package with detergent,anti-rust,-anti-oxidant and EP-action. The conditions of the shear testin theOpel pump were as follows:

Shear time: 24 hours Temperature: 50' C. Speed: 1500 r.p.m. Quantity ofoil: 800 g.

The results of the shear tests are shown in Table IV.

The behavior of the present polymers as dispersants was examined in aone-cylinder CLR engine. Lubricatnig oil compositions consisting of amineral lubricating oil with a V 100' C.==6.3 cs., which in addition toone of the present polymers contained 0.75%methylcne-bis-2,6-ditert-butylphenol and 1.0% by weight of triphenylphosphate. were subjected to a CLR MS Se- :1 test was also carried outwith a lubricating oil composition which contained a commercialdispernnt (a copolymer of alkyl methacrylates and N-vinyl pyrrolidone)instead of one of the present polymers.

The results of the engine tests are reported in Table V.

v to those of the invention but have ditierent C by weight of 4.4'- I 8Table V Engine sludge rating Composition of the oil: (='clean) Baseoil+1.5% of polymer 10 37.2 Base oil+2.i% of polymer 11 35.4 Baseoil+l.5% commercial additive 27.5

EXAMPLE VI The effect of the addition of extra initiator towards the Iend of the polymerization in the preparation of the acid copolymers isrepresented inthe following table.

l 0.05 after ti hrs. 8 0.01 aiter 8% hrs.

the base oils in the tests listed above have already been corrected witha view to the factthat the present polymers were not added to these baseoils as such but in the form of a 30%-concentrate in oil. 7

The foregoing dataclearly demonstrate the improved properties of thecompositions of the invention. The pour point test results shown inTable II indicate that while oopolymers having side chains with a C of12.0 (Polymer B) did not reduce the pour point of the base oil at all,and PolymerB having a C value of 15.0 decreased the pour point by only6" C., the polymers of the invention having C numbers ranging from l3.2to 14.1 decreased the pour point 20' C. or more. In view of therelatively poor performance of polymers A and B which are similar vaiuesit was quite remarkable'that polymers made in accordance with theinvention should proveto be so highly effective.

" The results shown in Table IV and V indicate that in addition tohaving improved pour points, the compositions of the invention also havegood shear stability and have dispersant properties superior to those ofa comparable commercial additive.

We claim as our invention:

1. A lubricant composition consisting essentially of a major amount of alubricating oil and a minor amount, from 1 to 10% by weight, of anoil-soluble copolymer of one or more alkyl esters of a C alpha,beta-'vinylidene monocarboxylic acid and one or more monohydroxy C alkylesters of C alpha, betavinylidene monocarboxylic acid; wherein at leastmole percent of the alkyl esters have CH (CH,),, groups, n being atleast 9, and the average number of carbon atoms of said groups is fromof the units derived from alkyl esters to those derived from hydrosyalkyl esters is 10 to l-3.

n being at least 9, V

9. The composition of claim 8 wherein the hydroxy- 4. The composition ofclaim 2 wherein the average number of carbon atoms in the CH,--(CH,),,-groups, n being at least 9, is from 13.0 to 14.1.

5. The composition of claim 3 wherein the monocarboxylic acid used toform the alkyl and monohydroxy alkyl esters is selected from the groupconsisting of methacrylic acid, acrylic acid and mixtures thereof.

7 6. The composition of claim 1 wherein the lubricating oil is a minerallubricating oil. v

7. The. composition of c1aim 5 wherein the monocarboxylic acid ismethacrylic acid.

8. The composition of claim number of carbon atoms in the CH;(CH,),,groups,

is from 13.0 to 14.1.

alkyl ester is ap-hydroxyethyl ester.

7 wherein the; average 10. The composition of claim 9 wherein thelubricating oil is a mineral lubricating oil.

References Cited UNITED STATES PATENTS 2,655,479 10/ 1953 Munday et al.252-56 2,993,032 7/1961 Stuart ct a1. 252-56X 3,222,282 1/1965 Berkowitzet al. 252-56X 3,249,545 5/ 1966 Van der Voort 252-- 56X 3,377,2854/1968 Randles 252-56 DANIEL E. WYMAN, Primary Examiner W. 1-1. CANNON,Assistant Examiner US. Cl. X.R.

